1. Field of the Invention
Both pressure-controlled and stroke-controlled injection systems can be used to deliver fuel into combustion chambers of autoignition internal combustion engines. Injection systems with high-pressure reservoirs have the advantage that the injection pressure can be adapted to the load and speed of the engine. A high injection pressure is required in order to reduce emissions produced and to achieve a high specific output of the engine. Since the pressure level that high-pressure fuel pumps can achieve in the high-pressure reservoir is limited for strength reasons, a pressure booster at the fuel injector can be used to boost pressure further in fuel injection devices with a high-pressure reservoir.
2. Prior Art
DE 199 10 907 A1 has disclosed a fuel injection device that has a pressure booster unit disposed between a pressure reservoir and a nozzle chamber. Its pressure chamber communicates with the nozzle chamber via a pressure line. A bypass line is also provided, which is connected to the pressure reservoir. The bypass line is connected directly to the pressure line. The bypass line can be used for a pressure injection and is disposed parallel to the pressure chamber so that it is continuously open independent of the movement and position of a movable lever of the pressure boosting unit.
DE 102 18 904.8 relates to a fuel injection device for internal combustion engines having a fuel injector which can be supplied from a high-pressure fuel source, and a pressure-boosting unit. The closing piston of the fuel injector protrudes into a closing pressure chamber so that the closing piston can be subjected to fuel pressure in order to produce a force that acts on the closing piston in the closing direction; the closing pressure chamber and the return chamber of the pressure boosting unit are constituted by a shared closing pressure/return chamber. All of the partial regions of the closing pressure/return chamber are permanently connected to one another to permit the exchange of fuel. The pressure boosters known from DE 199 10 970 A1 and DE 102 18 904.8 are actuated by means of an exertion of pressure on or relief of pressure in a return chamber of the pressure booster. Controlling a pressure booster via the return chamber is advantageous in terms of discharge losses and permits a simple triggering of the pressure booster by means a 2/2-way valve.
The disadvantage of the pressure boosters known from DE 199 10 970 A1 and DE 102 18 904.8 is the routing of the control bore for relieving the pressure in the return chamber of the pressure booster. Due to the fact that the control valve for the pressure booster is disposed above the pressure booster in most internal combustion engines for space reasons, it is necessary for the control line that is subjected to the fuel pressure prevailing in the high-pressure reservoir to be routed out of the return chamber of the pressure booster and past the pressure booster. This requires a larger outer diameter of the fuel injector into which the pressure booster is incorporated, as a rule in the head region, or requires an eccentric placement of the pressure boosting element that is disposed in the pressure booster and is, as a rule, embodied in the form of a piston. This previously required line routing resulted in bore intersections in the control line for exerting pressure on or relieving pressure in the return chamber of the pressure booster. As a rule, bore intersections involve high material stresses, which require costly machining steps and are detrimental to a durable design of a fuel injector.